It is well known that an aromatic primary amine color developing agent oxidized with exposed silver halide reacts with a coupler to form a dye such as an indophenol, an indoaniline, an indamine, an azomethine, a phenoxazine, a phenazine or a like dye, whereby a color image is formed. In this photographic system, the subtractive color process is ordinarily employed for color reproduction and color images are formed by yellow, magenta and cyan dyes.
In order to form cyan color images, phenolic or naphtholic couplers are generally employed. However, these couplers have a serious problem in that color reproducibility is remarkably deteriorated because dyes formed therefrom have an undesirable absorption in the green region. Accordingly, it has been desired to solve this problem.
In order to solve this problem, 2,4-diphenylimidazoles are disclosed in European Patent 249,453 A3. These couplers are preferred from the standpoint of color reproduction since they provide dyes which have a small amount of undesirable absorption on the shorter wavelength side in comparison with conventional dyes.
However, the couplers as described in European Patent 249,453 A3 have some disadvantages in practical use because they have still insufficient color reproducibility, in that they have a low coupling activity, and because the dyes formed therefrom have very poor fastness to heat and light.
Pyrazoloazole couplers as described in JP-A-64-552, JP-A-64-553, JP-A-64-554, JP-A-64-555, JP-A-64-556 and JP-A-64-557 (which correspond to U.S. Pat. No. 4,873,183) have improved undesirable absorption on the shorter wavelength side as compared with conventional dyes. However, their color forming property and color reproducibility are insufficient as cyan couplers.